As electronic devices become increasingly complex, there are more sub-circuits in electronic devices. Each of the sub-circuits may require different voltage to other sub-circuits and external power supply, for this reason, electronic devices need multiple DC-DC voltage converting circuits to convert voltage. DC-DC voltage converting circuits have various types such as DC-DC buck converter, DC-DC boost converter and inverse DC-DC converter. And according to circuit operation, there are isolated converter, non-isolated converter, forward converter and flyback converter. Conversion efficiency of DC-DC converter is crucial, and power controlling is the popular method to improve the conversion efficiency of the conventional DC-DC converter, e.g. pulse width modulation (PWM), pulse frequency modulation (PFM), pulse skipping, burst mode and off-time modulation.